st: identify unique string values within lists of elements over chosen time windows

st: identify unique string values within lists of elements over chosen time windows

Date

Thu, 21 Mar 2013 16:22:54 -0700 (PDT)

Hi everyone. I have an unbalanced, large panel dataset, where each observation
can take multiple string values (each string is stored in a separate variable).
At each point in time, I need to count whether the string value(s) taken by an
observation are "new" , meaning that they do not show up among the values taken
by the same observation in previous years. How should I approach this problem ?
Thanks ! Below is a description of data. I need to calculate newval
obs yr var1 var2 var3 newval
1 90 str1 str2 str3 3
1 91 str1 str4 str5 2
2 90 str3 str4 2
2 91 str4 str5 1
2 93 str3 str5 0
2 94 str7 1
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